The present invention relates to a structure for rotatably supporting a rotating member such as a gear and a pulley for transmitting a driving force to a driven member, on a fixed shaft on which the member rotates.
FIGS. 10a to 10d are sectional views showing various conventional structures for mounting a gear or a pulley on a fixed shaft on a chassis.
Referring to FIG. 10a, a chassis 52 made of resin or metal has a metal shaft 53 securely embedded therein, and a gear 51 is rotatably mounted on the shaft 53. A washer 54 is attached to the shaft 53 so that the gear 51 is prevented from moving upward in the axial direction of the shaft. Hence the gear 51 can be rotated without falling off from the shaft 53.
Referring to FIG. 10b, in another structure, a base 62 made of resin and having an integral shaft 63 is formed on a metal chassis (not shown) by outsert molding. A gear 61 is rotatably mounted on the shaft 63. The shaft 63 has a throughhole 64 at the center thereof, in which a screw 65 is engaged. Thus, the gear 61 is held by a head 651 of the screw 65 so as to be prevented from moving upward in the axial direction of the shaft. The gear 61 can be rotated without coming off from the shaft 63.
As shown in FIG. 10c, a base 72 of resin is formed on a metal chassis (not shown) by outsert molding. A shaft 73 having a hook 74 at the upper end thereof is integrally formed on the base 72, and a gear 71 is rotatably mounted on the shaft 73. The hook 74 prevents the gear 71 from moving upward in the axial direction of the shaft 73, thereby enabling the gear 71 to rotate without coming out of the shaft 73.
In a structure shown in FIG. 10d, a base 82 made of resin formed on a metal chassis (not shown) by outsert molding is provided with an upwardly extending integral shaft 86 in which a hole 83 is formed. A gear 81 made of resin and having a downwardly extending integral shaft 84 is inserted in the shaft 86 so as to be rotated therein. A hook 85 integral with the shaft 84 is provided at the lower end thereof, so that when the gear 81 is mounted, the hook 85 projects out of the hole 83 and engages with the bottom of the base 82, thereby holding the shaft in the hole 83. Thus the gear 81 is prevented from falling off from the base 82 at rotation.
Referring to FIG. 10e, on a metal chassis 92, a base 93 is formed by outsert molding. The base 93 has an integral shaft 94, the upper end of which is formed into a projection 941. A gear 91 is rotatably mounted on the shaft 94. A holder 95 is further formed on the chassis 92 by outsert molding adjacent the base 93. The holder 95 abuts on the projection 941 of the shaft 94 so that the movement of the gear 91 in the axial direction of the shaft is restricted, thereby enabling to rotate the gear 91 without the gear falling off from the shaft 94.
The structure shown in FIG. 10a requires a large number of parts. Moreover, operations for securely attaching the shaft 53 to the chassis 52 and for mounting the washer 54 on the shaft 53 are necessary, so that the manufacturing process cannot be reduced, thereby increasing the manufacturing cost.
In the case of the structure of FIG. 10b, a long time is consumed to attach the screw 65 in the throughhole 64 of the shaft 63. Thus the structure is not suitable for mass production. In addition, when the screw 65 is fastened with excessive force, the shaft 63 may be broken.
In the structure shown in FIGS. 10c and 10d, in order to form the hook 74 or 85 with resin, the structure of the mold for producing the base becomes complicated. If the mold comprises a plurality of parts, the assembled mold causes differences in levels of the surfaces of the base. Hence the rotation of the gear is impaired.
The structure of FIG. 10e involves a large number of parts and a complicated assembling operation so that the manufacturing cost is increased.